(1) Field of the Invention
The present invention relates to a granular calcium hypochlorite composition which does not decompose but remains stable even when stored for a long time or exposed to a high temperature, in which dusting does not occur, and which has an excellent solubility, and to a process for the preparation of this granular calcium hypochlorite composition
(2) Description of the Related Art
Calcium hypochlorite is a strong oxidizer and is a valuable compound widely used for sterilizing and disinfecting swimming pool water, water supply or drainage water and public bath water or the like, or as a bleaching agent for cotton, pulp or the like, because of its high sterilizing and bleaching effects.
A composition composed mainly of calcium hypochlorite is commonly called "high test hypochlorite", and the composition is marketed under the name of 65 wt.% or 70 wt.% high test hypochlorite in accordance with the available chlorine content.
The high test hypochlorite is formed into powders, granules, and tablets The granular product is obtained by granulating the powder, is easy to handle, is used for sterilizing or disinfecting swimming pool water or service water, and is consumed in a largest quantity.
High test hypochlorite generally comprises at least 65% by weight of calcium hypochlorite, 3 to 20% by weight of water, 2 to 10% by weight of calcium hydroxide, components incorporated in the preparation process, such as calcium chloride, calcium carbonate and calcium chlorate, and sodium chloride, as the diluent. The calcium hypochlorite composition undergoes little decomposition and has a high stability in the anhydrous state. But, abrupt decomposition will occur due to contact with a flame, spark, or an organic substance and the composition has a poor safety factor. To improve the safety, water is incorporated in an amount of 3 to 20% by weight, but the presence of water has an adverse effect on the stability of the calcium hypochlorite composition. Namely, the composition is easily decomposed if the water content is increased or the temperature is elevated. To maintain a good stability in the presence of this water, calcium hydroxide is incorporated as a stabilizer in an amount of 2 to 10% by weight. But the addition of calcium hydroxide exerts an undesired function of controlling the speed of dissolution of high test hypochlorite in water, and if calcium hydroxide is added in a large amount, dusting occurs and calcium hydroxide remains in the form of a water-insoluble residue. Furthermore, since calcium hypochlorite and calcium hydroxide are mixed together in the powdery state, various handling and preparation problems arise, for example, with regard to the mixing means and the homogeneousness of the formed mixture.
The main object of use of high test hypochlorite is to sterilize and disinfect swimming pool water and service water, and for this purpose, the high test hypochlorite composition is required to have preferred properties such that the safety and stability are high, dusting does not occur, the composition is promptly dissolved and no water-insoluble residue remains. But, as pointed out hereinbefore, the addition of calcium hydroxide is practically indispensable for improving the stability. Furthermore, since calcium hypochlorite is in the form of a fine powder, the granulation step of compression-molding the fine powder into a granular product is indispensable to prevent dusting, and since a hard granular product is formed by molding, the solubility is further reduced practically.